1. Field of the Invention
The present invention relates to a processing chamber and a method for centering a substrate therein.
2. Description of the Prior Art
In the manufacturing of integrated circuits, liquid crystal displays, flat panels and other electronic devices, multiple layers of materials are deposited onto and etched from substrates. The processing systems for manufacturing said devices typically include several vacuum processing chambers connected to a central transfer chamber to keep the substrate in a vacuum environment. Several sequential processing steps, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), etching, and annealing, can be executed in said vacuum processing chambers respectively.
The substrates can be delivered from the transfer chamber to said processing chambers via transfer mechanisms (e.g. robot blade) and be placed on a support structure (e.g. susceptor or pedestal) of each processing chamber for processing. The transfer mechanisms can also transfer the substrate from one of the processing chambers to another. Moreover, the transfer mechanisms can slide underneath the back side of the substrate and then lift the substrate off the support structure without causing damage to either the support structure or the substrate. To facilitate the transportation of the substrate, a plurality of supporting members such as, for example, supporting pins, are disposed on the top surface of the support structure to lift the substrate apart from the top surface to create a space between the back side of the substrate and the top surface for the operation of the transfer mechanisms.
The processing of large glass substrates utilized for displays is in some ways similar to the processing of other types of substrates such as semiconductor wafers. Such glass substrates, however, are often larger than typical silicon wafers. For example, glass substrates may have a plane area greater than 600 mm×720 mm, to permit the formation of suitable displays. The utilization of large glass substrates introduces complexities into processing that may not be present when processing other types of substrates. For example, in addition to their size, glass substrates employed for displays are typically rectangular. The large size and shape of glass substrates can make them difficult to transfer from position to position within a processing system when compared with smaller, circular substrates. Consequently, systems for processing glass substrates generally require larger chambers, apertures, and transfer mechanisms. The need for larger chamber sizes to handle large substrates also leads to a requirement for larger and more powerful vacuum pumps, power supplies, control mechanisms and the like and a corresponding increase in system cost.
In addition, for proper set-up, calibration, and debugging of the automated movement of a substrate into and out of a processing chamber, and for proper deposition effect, alignment of the substrate to the susceptor is essentially required. A substrate aligning device was disclosed in U.S. Pat. No. 5,611,865, issued Feb. 14, 1996, by White et al. It is disclosed that by disposing a plurality of wedge shaped structures on the top flat surface of the supporting pin at the different corner of the susceptor, the substrate can be aligned to the center by the weight of the substrate itself.
However, as the supporting pins are only disposed on the corners of the susceptor, the size of the gap between the supporting pins increase with the size of the glass substrate, the stress inside the glass may be too large for the glass to bear due to the fracture of the substrate. When the size of the glass substrate is too large, the substrate sags under its own weight on the supporting pins. The sagging substrate causes gas to be trapped between the substrate and the susceptor surface as the substrate is lowered on the susceptor. The trapped gas may create a gas cushion that allows the substrate to move laterally over the susceptor, thus creating misalignment even if the substrate was previously aligned prior to being placed on the susceptor.
Therefore, a need exists for centering a substrate, especially a large substrate, in a processing chamber that prevents the above-mentioned problems.